This application is related to and claims priority from Japanese Patent Applications No. 2002-30924 filed on Feb. 7, 2002 and No. 2002-182872 filed on Jun. 24, 2002, the contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to an ejector decompression device for a vapor compression refrigerant cycle. More specifically, the present invention relates to an ejector with a throttle controllable nozzle in which a throttle degree can be controlled.
2. Description of Related Art
In an ejector cycle, pressure of refrigerant to be sucked into a compressor is increased by converting expansion energy to pressure energy in a nozzle of an ejector, thereby reducing motive power consumed by the compressor. Further, refrigerant is circulated into an evaporator by using a pumping function of the ejector. However, when energy converting efficiency of the ejector, that is, ejector efficiency xcex7e is reduced, the pressure of refrigerant to be sucked to the compressor cannot be sufficiently increased by the ejector. In this case, the motive power consumed by the compressor cannot be satisfactorily reduced. On the other hand, a throttle degree (passage opening degree) of the nozzle of the ejector is generally fixed. Therefore, when an amount of refrigerant flowing into the nozzle changes, the ejector efficiency xcex7e is changed in accordance with the change of the refrigerant flowing amount. Further, according to experiments by the inventors of the present invention, if the throttle degree of the nozzle is simply changed, the ejector efficiency xcex7e may be greatly reduced due to a refrigerant flow loss of a control mechanism for controlling the throttle degree.
In view of the foregoing problems, it is a first object of the present invention to provide an ejector decompression device having a throttle controllable nozzle with an improved structure.
It is a second object of the present invention to variably control a throttle degree of a nozzle of the ejector decompression device without largely reducing ejector efficiency xcex7e of the ejector decompression device.
According to the present invention, an ejector decompression device for a refrigerant cycle includes a nozzle for decompressing and expanding refrigerant flowing from a radiator by converting pressure energy of refrigerant to speed energy of the refrigerant, a pressure-increasing portion that is disposed to increase a pressure of refrigerant by converting the speed energy of refrigerant to the pressure energy of refrigerant while mixing refrigerant injected from the nozzle and refrigerant sucked from an evaporator of the refrigerant cycle, and a needle valve disposed to be displaced in a refrigerant passage of the nozzle in an axial direction of the nozzle for adjusting an opening degree of the refrigerant passage of the nozzle. Here, the refrigerant passage is defined by an inner wall of the nozzle. Further, the nozzle includes a throat portion having a cross-sectional area that is smallest in the refrigerant passage of the nozzle, and an expansion portion in which the cross-sectional area is increased from the throat toward downstream in a refrigerant flow. In the ejector decompression device, the needle valve and the inner wall of the nozzle are provided to have predetermined shapes so that refrigerant flowing into the nozzle is decompressed to a gas-liquid two-phase state at upstream from the throat portion in the refrigerant flow. In the present invention, because refrigerant is decompressed to the gas-liquid state at upstream from the throat portion, refrigerant bubbles are generated, and a mass density of the refrigerant is reduced. Accordingly, the cross-sectional area of the refrigerant passage is relatively reduced in the nozzle. Thus, the flow amount of refrigerant can be adjusted, and the refrigerant passage can be prevented from being throttled more than a necessary degree. As a result, ejector efficiency xcex7e can be prevented from being largely reduced in the ejector decompression device having the nozzle where the opening degree of the refrigerant passage can be variably controlled.
Alternatively, the needle valve is disposed in the refrigerant passage of the nozzle to define a throttle portion having a cross-sectional area that is smallest in a space between the needle valve and the inner wall of the nozzle, and the throttle portion is positioned upstream from the throat portion in the refrigerant flow. Therefore, rectified refrigerant with a small disturbance can pass through the throat portion, and is sufficiently accelerated more than the sound speed while flowing through the extension portion. Because the refrigerant can be accurately sufficiently accelerated in the nozzle, the ejector efficiency can be effectively improved.
Preferably, the needle valve has a downstream portion that is tapered toward a downstream end of the needle valve so that a cross-sectional area of the downstream portion of the needle valve is reduced toward the downstream end, and the inner wall of the nozzle is formed into an approximate cone shape having at least two different taper angles, upstream from the throat portion. Further, the inner wall of the nozzle has a radial dimension that is reduced toward the throat portion. Alternatively, the inner wall of the nozzle has a radial dimension that is reduced from an upstream end of the nozzle toward the throat portion and is increased from the throat portion toward a downstream end of the nozzle.